Energy Sources, Part A, 33:1949–1959, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1556-7036 print/1556-7230 online
DOI: 10.1080/15567030903436830
Bioplastics and Petroleum-based Plastics:
Strengths and Weaknesses
F. GIRONI1 and V. PIEMONTE1
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1
Department of Chemical Engineering, Materials & Environment,
University of Rome, Rome, Italy
Abstract The application of biomass, such as starch, cellulose, wood, and sugar,
used to substitute fossil resources for the production of plastics, is a widely accepted
strategy towards sustainable development. In fact, this way a significant reduction
of non renewable energy consumption and carbon dioxide emission is accomplished.
In recent years, several typologies of bioplastics were introduced and the most important are those based on cellulosic esters, starch derivatives, polyhydroxybutyrate,
polylactic acid, and polycaprolactone. Nowadays, the most important tool to evaluate
the environmental impact of a (bio)plastic is the life cycle assessment that determines
the overall impact of a plastic on the environment by defining and analyzing several
impact categories index like the global warming; the human toxicity; the abiotic
depletion; the eutrophication; the acidification; and many others directly related to
the production, utilization, and disposal of the considered plastics. The aim of this
work is to present a comparison between bioplastics and conventional plastics through
the use of the “Life Cycle Assessment” methodology. In particular, the life cycle
assessment’s Cradle to Grave of shoppers made from Mater-Bi (starch-based plastic)
an polyethylene were reported and compared as a case study in order to highlight
the strengths and weaknesses of the bioplastics and the conventional plastics.
Keywords bioplastics, environmental impact, mater-bi, life cycle assessment, renewable resources
1. Introduction
Nowadays the worldwide production of bioplastics is about 750,000 tons/year and is
very modest when compared with 200 million tons/year of conventional plastics derived
from petroleum; it is estimated that in the near future, the growth will be exponential,
reaching about 1,000,000 tons/year in 2011 (Widdecke et al., 2008). The major manufacturers are Nature Works (with a production of 140,000 tons/year of polylactic acid
[PLA]) and Novamont (with a production of 35,000 tons/year of Mater-bi, starch-based
bioplastics).
The interest in the development of biodegradable plastics noticed in recent years is
due to motives of both environmental and strategic nature (Zhang et al., 2000; Demirbas,
2007; Anderson et al., 1998; Gross and Kalra, 2002). As a matter of fact, in order to
reduce the environmental impact of plastics (especially in terms of CO2 released in the
environment) some of the products obtained from agriculture (starch, cellulose, wood,
Address correspondence to Dr. Vincenzo Piemonte, Department of Chemical Engineering,
Materials & Environment, University of Rome, via Eudossiana 18, Rome 00184, Italy. E-mail:
piemonte@ingchim.ing.uniroma1.it
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sugar) are used as raw materials. This way the net balance of carbon dioxide is greatly
reduced, since the CO2 released during production, utilization, and disposal of plastics
is balanced by the CO2 consumed during the growth cycle of the plant. Furthermore,
petroleum, with a constantly rising price, is replaced by renewable raw materials obtained
from agriculture.
Several biopolymers are produced from fermentative processes of natural valuable
raw materials, such as wheat, corn, sugar, rice, potatoes, and soya. Specific consumption
per unit of biodegradable plastic produced is different (Harding et al., 2007) depending
on the raw material used, but there is no doubt that these raw materials will be taken away
from other uses, in particular from alimentation, with a consequent increase in the cost
of food. From this point of view, it is clear that the development of bioplastics requires
the use of less valuable raw materials, such as agricultural or food industry wastes or
from the use of non edible genetically modified plants, which may be grown in lands
(e.g., mountains) not suitable for the production of food.
The use of bioplastics was also stimulated by a second environmental motive, related
to problems connected with the disposal of waste: in the 1990s, the main system for the
disposal of municipal solid waste (with a fraction of plastics equaling 20–30%) was the
disposal in landfill. Traditional plastics undergo degradation phenomena with very slow
kinetics; hence, the volume required by these materials in landfills is virtually stable over
time. On the contrary, bioplastics show higher degradation rates in landfills (Ishigaki
et al., 2004) and, therefore, the required volumes can be contained.
Currently the market suggests several typologies of bioplastics, among which the
most important are those based on cellulosic esters (Hoppenheidt and Trankler, 1995),
starch derivatives (TPS) (Bastioli, 2005), polyhydroxybutyrate (PHB) (Harding et al.,
2007), polylactic acids (PLA) (Tokiwa and Calabia, 2006), and polycaprolactone (PCL)
(Demirbas, 2007). Application fields range from uses in the pharmaceutical and biomedical area as potential biocompatible materials for artificial protheses, for sutures, and
as a medium for controlled drug release; in the field of packaging, including food and
shoppers; and in the field of agriculture as mulching films (Widdecke et al., 2008).
Nowadays, the development of bioplastics is hampered by higher costs of production
of these materials as opposed to traditional plastics; however, a thorough analysis considering not only the cost of production but also the costs associated with the managing
of waste might lead to various results.
In this article, the main features of bioplastics will be discussed, highlighting the
problems linked with their biodegradation and with possible scenarios for their disposal.
Therefore, in order to provide first considerations on the strengths and weaknesses of
the conventional plastics and bioplastics, the results reported in different literature life
cycle assessments (LCAs) studies (Harding et al., 2007; Hoppenheidt and Trankler,
1995; Bastioli, 2005; Patel, 2002; Krueger et al., 2009) were analyzed and discussed.
Furthermore, an original “cradle to grave” LCA study (from the raw materials up to the
final disposition of the analyzed product) focused on the comparison between shoppers
made from Mater-Bi and polyethylene (PE) is reported as a Case Study.
2. The Biodegradability Matter
In accordance with ASTM D 6400, biodegradable plastics are only those whose degradation occurs as a result of natural action of microorganisms, such as bacteria, fungi, and
algae, in a limited period of time and in absence of ecotoxic effects.
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Bioplastics vs. Petroleum-based Plastics
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Aerobic or anaerobic biodegradation may occur and the process that completely
degradates the polymer into biomass is called “Complete Biodegradation,” while if the
original polymer is completely converted in gas and minerals we have a “Mineralization.”
In any case, the biodegradation takes place in two phases: an initial phase in which
microorganisms launch a chemical attack on the polymer chain aimed at the breaking
of chemical bonds, and a second phase of real biodegradation. These two phases are
strongly controlled by the presence of numerous factors, both endogenous (as molecular
weight, crystallinity, flexibility of the molecule) and exogenous (temperature, humidity,
pH, availability of oxygen, enzymatic activity) that can, therefore, alter and/or modify
the outcome of the biodegradation process itself (Kale et al., 2007b).
As reported by Davis and Song (2006), the most favorable final disposition, from
an environmental point of view, for a bioplastics is represented by the composting
process that transforms, by a biodegradation process, the disposed product into a soillike substance called humus, CO2 , water, and inorganic compounds and leaves no visible,
distinguishable, or toxic residues. Indeed, with regard to recycling, nowadays processes
for selecting and recycling bioplastics are not yet developed, despite what happens
for conventional plastics. The composting of bioplastics can, therefore, be an optimal
solution, taking into account that the process conditions in terms of temperature, humidity,
oxygen, etc. must be strictly controlled if we want to achieve appreciable results in terms
of final products. The work of Kale et al. (2007a) concerning the biodegradation of PLA
bottles under controlled and natural conditions is interesting. The experimental results
show that the efficiency of degradation in a natural environment is equal to approximately
10–20% of efficiency in a controlled environment.
Additives are often present in the bioplastics, mainly to improve the mechanical
properties of the obtained material. This choice may not only cause a reduction in the
biodegradability of plastics and other serious ecotoxic effects, but it might even determine
the non-compostability of the bioplastic, making in fact, a vain every advantage achievable
through the use of a bioplastic.
3. Bioplastics and Petroleum-based Plastics:
How to Compare?
If on the one hand, the real biodegradation of a plastic represents an extremely delicate
problem, certainly a key aspect in assessing the applicability or not of bioplastics is the
impact on the environment resulting from their use, during the entire life cycle from
production to final disposal (cradle to grave). This type of analysis is called Life Cycle
Analysis (LCA) and is based on finding some factors considered crucial in assessing the
impact that a particular product can have on the environment. Among the most important
factors or indices of environmental impact there are:
Abiotic depletion: the characterization factor is the potential of abiotic depletion of the
extraction of those minerals and fossil fuels. The unit of the characterization factor
is kg of antimony (Sb) equivalents per kg of extracted mineral.
Global warming: the characterization factor is the potential of global warming of each
greenhouse gas emission to the air. The unit of the characterization factor is kg of
carbon dioxide (CO2 ) equivalents per kg of emission.
Human toxicity: the characterization factor is the potential of human toxicity of toxic
substances emitted to the air, water, or/and soil. The unit of the characterization
factor is kg of 1,4-dichlorobenzene (1,4-DB) equivalents per kg of emission.
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Fresh water aquatic ecotoxicity: the characterization factor is the potential of fresh water
aquatic toxicity of each substance emitted to the air, water, or/and soil. The unit of
this factor is kg of 1,4-DB equivalents per kg of emission.
Marine aquatic ecotoxicology: the characterization factor is the potential of marine
aquatic toxicity of each substance emitted to the air, water, or/and soil. The unit
of this factor is kg of 1,4-DB equivalents per kg of emission.
Terrestrial ecotoxicity: the characterization factor is the potential of terrestrial toxicity of
each substance emitted to the air, water, or/and soil. The unit of this factor is kg of
1,4-DB equivalents per kg of emission.
Photochemical oxidation: the characterization factor is the potential of photochemical
ozone formation of each substance emitted to the air. The unit of this factor is kg of
ethylene (C2 H4 ) equivalents per kg of emission.
Acidification: the characterization factor is the acidification potential for each acidifying
emission to the air. The unit of this factor is kg of sulfur dioxide (SO2 ) equivalents
per kg of emission.
Eutrophication: the characterization factor is the potential of eutrophication of each
eutrophying emission to the air, water, and soil. The unit of this factor is kg of
phosphate ion (PO4-) equivalents per kg of emission.
Tables 1 and 2 show a collection of LCA literature data (Patel, 2002, 2005); each
LCA characterizes and compares the environmental impact of various bioplastics (thermoplastic starch (TPS), polylactic acid (PLA), and polyhydroxyalkanoates (PHA) and
traditional plastics (high and low density polyethylene, Nylon 6, polyethylene terephtalate (PET), polystyrene (PS), polyvinyl alcohol (PVOH) and polycaprolactone) with an
approach cradle to grave. The comparison is given on the basis of some of the most
important indices of environmental impact cited above.
Table 1
Energy required from non-renewable sources and CO2 emissions for different types of
plastics currently on the market
Type of plastic
From non-renewable sources
HDPE
LDPE
Nylon 6
PET
PS
PVOH
PCL
From renewable sources
TPS
TPS C 15% PVOH
TPS C 60% PCL
PLA
PHA
Energy
requirement, MJ/kg
Global
warming, kg CO2 eq/kg
80.0
80.6
120.0
77.0
87.0
102.0
83.0
4.84
5.04
7.64
4.93
5.98
2.70
3.10
25.4
24.9
52.3
57.0
57.0
1.14
1.73
3.60
3.84
Not Available
Bioplastics vs. Petroleum-based Plastics
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Table 2
Eutrophication and acidification for different types of
plastics currently on the market
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Type of plastic
Pellets
LDPE (1 kg)
TPS (1 kg)
Starch foam (1 kg)
Starch film (1 kg)
Loose fills
Starch foam (1 m3 D 10 kg)
PS foam (1 m3 D 4 kg)
Films and bags
TPS (100 m2 )
Starch-polyester (100 m2 )
PE (100 m2 )
a (g
b (g
Acidificationa
Eutrophicationb
17.4
10.9
20.8
10.4
1.1
4.7
2.8
1.1
276.0
85.0
39.0
8.0
239.0
26.5
236.0
103.0
2.8
15.0
SO2 eq).
PO34 eq).
Overall, the data reported in Tables 1 and 2 show how the production and use
of bioplastics is more advantageous compared to conventional plastics from the energy
demand and emissions of greenhouse gases point of view. On the contrary, they have
a strong impact on the environment for acidification of soil and the eutrophication,
mainly because of the use of fertilizers and chemicals in the cultivation of renewable
raw materials used for the production of bioplastics. However, it should be pointed out
that the presence of non-biodegradable copolymers in bioplastics (see Table 1) decrees a
significant increase in energy demand and CO2 emissions compared to bioplastics. Indeed,
in an attempt to improve the performance of mechanical biopolymers, non-biodegradable
copolymers are added thus reducing the biodegradable power of the obtained material. It is
important to stress that the results of above LCA were obtained using the incineration with
energy recovery as final provision: this choice is not particularly favorable to bioplastics
mainly for their low calorific value.
The analysis of LCA data, always show that bioplastics have some indices of
environmental impact lesser than those of other traditional plastics, while other indices
are in favor of the latter; hence, the need to determine an index of overall environmental
impact where all indices can be incorporated and adequately weighed.
To that end, there are various methods for weighting factors of environmental impact,
aimed precisely to the determination of a single global index. One of the methods most
often used in the LCA is called “distance-to-target” (Weiss et al., 2007), which deals
directly a pair of plastics to compare (for example PLA and PE) providing a single index
of environmental impact on the pair itself.
In this regard, Figure 1 shows the value of the cumulative index of environmental
impact for a couple of products of commercial interest. Zero values of this index indicate
a substantial “balance” between the two materials in terms of environmental impact.
Positive values indicate a conventional plastic superiority, while negative values
indicate a lower environmental impact of bioplastics. The data seem to be entirely in
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Figure 1. Values of the overall environmental impact for several plastic-bioplastics pairs evaluated
with the “distance to target methodology.” (color figure available online)
favor of bioplastics, with the exception of two cases (regarding packaging with PLA and
loose-fills-based starch compared with polystyrene). However, since that methodology
defines the weight of the various indices of environmental impact depending on the
target of each index, it is clear that the results are strongly influenced by the criteria of
choice and priorities that are given to each category of environmental impact.
Another possibility to give an overall impact index is to group the impact categories
into three macro-categories: Human Health, Ecosystem Quality, and Resources as proposed by the Ecoindicator-99 methodology (Goedkoop et al., 2000). Then we must assign
a weight to the individual macro-category and define a global index of the impact I given
by:
X
I D
pi c i ;
i
where pi is the assigned weight to the macro-category of impact i and ci is the value of
the macro-category of impact. The result in terms of convenience of a conventional or a
new generation product is a function of the importance that will be assigned to individual
macro-categories.
Representing the three categories in a “mixing diagram” (Figure 2), each point within
the triangle represents a weighting combination. In each point of the mixing triangle, the
relative weights always add up to 100%. Therefore, the weighting question is, how much
weight out of 100% is attached to each of the three safeguard subjects. In a mixing
triangle, each corner represents a weight of 100% for one safeguard subject; in Figure 2,
the top corner is the weighting combination where “Ecosystem Quality” is weighted
100%, and 0% weight is given to both “Human Health” and “Resources.” Opposite
each corner is the 0%-weight line for this safeguard subject: Any point on the base of
the triangle of Figure 2 gives 0% weight to “Ecosystem Quality,” and the weights are
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Bioplastics vs. Petroleum-based Plastics
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Figure 2. Weighting problem: triangle diagram solution. (color figure available online)
split between “100% Human Health/0% Resources” in the bottom-left corner to “0%
Human Health/100% Resources” in the bottom-right corner. We only consider positive
weights, that is, a positive impact score always means a damage: only points within
the mixing triangle are taken as reasonable weighting sets. The figure shows two sets of
weights corresponding to point A (60% Ecosystem Quality, 20% Human Health, and 20%
Resources) and B (40% Ecosystem Quality, 30% Human Health, and 30% Resources). In
the A condition it is more convenient to use Product 1 while in the B one it is preferable
to use Product 2: the focus on one or other product is a function of the weight that will
be assigned to individual macro-categories of impact. The border area between the two
regions is the so-called “line of indifference” that is the set of values of the weights
assigned to bring the two products tested to have the same overall impact index, and thus
a condition of substantial equilibrium between the two products analyzed.
4. Case Study: Mater-Bi vs. PE Shoppers
In the following, we compare the results obtained from our LCAs on shoppers made
from Mater-bi and PE using the Ecoindicator-99 methodology (Goedkoop et al., 2000).
This LCA methodology considers 11 impact categories: Carcinogens, Respiratory Organics, Respiratory Inorganics, Climate Change, Radiation, Ozone Layer, Ecotoxicity,
Acidification/Eutrophication, Land Use, Minerals, and Fossil Fuels. The first six impact
categories are then be normalized and grouped in the macro-category “Human Health”
that considers the overall impact of the emissions associated to the product analyzed
on the human health; the categories Ecotoxicity, Acidification/Eutrophication, and Land
Use flow in the macro-category “Ecosystem Quality” considers the overall damage on the
Environment, while the “Minerals” and “Fossil Fuels” are grouped in the macro-category
“Resources” that accounts for the depletion of non renewable resources.
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The LCAs were performed by using the SimaPro7 software, while the data of LCIs
were taken both from the Ecoinvent v.2 and the Buwal 250 libraries. The data about the
Mater-Bi production (provided directly from Novamont, with data relating to production
in Terni, Italy) are updated to 2004 (Ecoinvent v2) and refers to a co-polymer with a
starch content of 35% and the left 65% are biodegradable polyester derived from non
renewable sources (polyester type not specified). For the PE, the production process of
granules was performed on average data, for various production sites throughout Europe,
contained in the Eco-profiles prepared by the European Plastics Industry (Buwal 250,
data updated to 2002).
The main assumptions made to perform the LCAs are:
Nature is not part of the production system, this implies that all the emissions
(fertilizers, pesticides, etc.) relative to the area allocated for agricultural production are
strictly taken into account.
As for the biodegradable polyester contained in the co-polymer Mater-Bi, it has been
considered the PCL (biodegradable polyester made from fossil fuels) (Demirbas, 2007).
The production of Mater-Bi and PE shoppers is achieved through three phases:
Production of granules, transportation of granules in the processing establishments, and
process of production of the shoppers by blow foil extrusion.
The LCAs have been realized on the basis of 1,000 shoppers made from Mater-Bi
(total weight of 68 kg) and PE (total weight of 52 kg), respectively. The different weight
between the two shoppers is due to different mechanical properties of the Mater-Bi and
PE, that is to obtain shoppers with the same mechanical characteristics, different thickness
of polymer films are needed (Davis, 2003).
The composting process has been chosen as the best disposal scenario for the
shoppers made from Mater-Bi. In particular, it was considered a degradation of Mater-Bi
by 60% (the remaining 40% is divided between biomass and recalcitrant residue) in the
presence of oxygen, such that 95% of the degraded carbon evolves in CO2 . The remaining
5%, assuming the presence of small anaerobic pockets (due to not perfect mixing of the
medium) is considered to evolve in CH4 (Hofstetter et al., 2008). Furthermore, the model
provides the treatment of the collected water in appropriate facilities and municipal waste
disposal by incineration for not composted wastes, including relative emissions.
The Recycling was chosen as the best disposal scenario for the shoppers made from
PE. The production efficiency of PE granules from recycled waste is about 90% (1 kg
recycled shoppers produce 0.9 kg of granules). Transportation and energy are considered
requirements of the selection and reprocessing processes. Furthermore, we assume that
the material obtained downstream of the process is being used for production in place of
virgin material.
The results of the LCAs “cradle to gate” are reported in Figures 3 and 4 in terms of
macro-categories of damage and mixing diagram for the weighting.
Figure 3 shows how the production of Mater-Bi shoppers has a strong impact in
terms of damage to quality of the ecosystem (it is worth noting that this macro-category
includes the impact categories “acidification,” “eutrophication,” “ecotoxicity,” and “land
occupation”). On the contrary, the effects on human health are roughly the same for
both Mater-Bi and for PE. Finally, from Figure 3 it is evident that the greater damage,
in terms of consumption of non-renewable resources (like petroleum-based resouces), is
determined by the shoppers made from PE with respect to that made from Mater-Bi.
The diagram of Figure 4 shows how the two products, using the set of weights
suggested by the LCA Suisse group (40% Human Health, 40% Ecosystem Quality, and
20% Resources) (Krueger et al., 2009), are roughly equivalent in terms of environmental
Bioplastics vs. Petroleum-based Plastics
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Figure 3. Comparison LCA “cradle to gate” on the production of Mater-Bi and PE shoppers.
(color figure available online)
impact. On the one hand, the bioplastics allow saving in terms of fossil resources, on the
other hand, they cause more damage in terms of the ecosystem since the use of different
chemicals (pesticides, herbicides, fertilizers) is particularly harmful both for humans and
the environment.
As for the disposal scenarios of the two products, a very interesting result was
obtained considering the comparison of the LCAs cradle to grave reported in Figure 5. As
you can see from the figure, the Mater-Bi shoppers show a higher impact respect to the PE
shoppers for all three damage categories; hence, all the possible weighting sets provide
the same result: the recycling of the PE shoppers have a lower overall environmental
impact than the Mater-Bi shoppers. The advantages, in terms of environmental impact,
derived from the saving of the non renewable resources that can be achieved by the
Figure 4. Weighting problem: comparison between Mater-Bi and PE shoppers. (color figure available online)
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Figure 5. Comparison LCA “cradle to grave” for the composting of Mater-Bi shoppers and the
recycling of PE shoppers. (color figure available online)
recycling of a conventional plastic are much higher than the advantages derived from
the production of compost. On the other hand, materials that can only have a certain
destination, such as the plastic used for bags for the collection of organic wastes, remain
outside of this type of consideration. In this case, the final destination can only be the
composting together with organic waste itself.
5. Conclusions
The literature studies show, in general, a superiority of bioplastics in terms of consumption
of non-renewable sources and emissions of greenhouse gases, whereas it would be preferable for conventional plastics with regard to the impact indices related to acidification and
eutrophication. Obviously, depending on the weight given to the various indices of environmental impact, we may give preference either to bioplastics or conventional plastics.
The LCA studies conducted to compare the environmental impact of the Mater-Bi
with that of a conventional plastic, such as PE, in terms of impact associated with the
production of the shoppers, yield a result only apparently controversial: the comparison
appears almost at par. This result must be interpreted considering that, if on one hand, the
bioplastic can save in terms of fossil resources, the other causes major damage in terms
of ecosystem quality because for the production of raw material (corn) it is necessary to
use an intensive agriculture with the use of different chemicals (pesticides, herbicides,
fertilizers) that are harmful to the environment. The superiority of the Mater-Bi on the
PE does not seem so obvious, but on the contrary, giving a high weight to both “human
health” and “ecosystem quality” the Mater-Bi “failed” in comparison. This result can
be generalized to other pairs of bioplastics/conventional plastics with close areas of
employment, such as PET and PLA. Therefore, the true advantage of the bioplastics is
represented by the use of renewable resources, but the benefit is paid in environmental
terms due to the impact on ecosystem quality caused by the use of pesticides and fertilizers
and by the consumption of land and water.
As for the disposal scenarios, the comparison of the LCAs cradle to grave for the
two products analyzed has pointed out the superiority, in terms of overall environmental
impact, of the recycling of conventional plastics on the composting of bioplastics. On
the other hand, the LCAs performed do not consider the advantages derived from the use
of biodegradable products, such as bags for the collection of organic wastes or cuterly
disposable, that can be disposed directly with the organic wastes avoiding the energetic
and logistical costs of the processes of collection and sorting of the wastes.
Bioplastics vs. Petroleum-based Plastics
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Acknowledgments
The authors wish to thank CONAI for their useful contributions.
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